Ad spending at national cable networks has jumped 42 percent since 2007, reaching the same level as broadcast networks, a Nielsen report indicates.

According to Nielsen, national cable networks--such as TBS, ESPN and MTV--generated $21 billion in ad revenue last year, just shy of the $21.1 billion in ad spending at broadcast networks such as ABC, CBS, Fox and NBC.

Total spending on TV ads increased by 4.5 percent in 2011 to $72 billion, Nielson found.

Automotive was the biggest advertising category in terms of spending on all media, Nielsen said. Auto brands spent $10.2 billion on advertising in 2011, more than twice the amount spent by fast-food brands, which was the second largest category.

AT&T was the biggest media buyer in 2011, shelling out $1.1 billion on ads. It was followed by Verizon, which spent $702 million on ads, Nielsen said.